MOSCOW, Oct 27 (Reuters) - Three prominent opponents of
Russian President Vladimir Putin were briefly detained at a
protest in central Moscow on Saturday that followed the first
meeting of a new opposition body elected in an online vote.

Police arrested politicians Alexei Navalny, Ilya Yashin and
Sergei Udaltsov as they tried to take part in a march of several
dozen opposition supporters after the inaugural session of the
newly-formed Coordination Council.

The opposition group, which met in a Moscow cafe, is tasked
with trying to mount a structured challenge to Putin, who
assumed the presidency in May for a six-year term.

"They gave us the mandate of trust and made us responsible
for coordinating efforts of dozens, hundreds, thousands and
millions of people who want positive changes in our country,"
said Navalny, a popular blogger who collected most of the votes.

While Putin has faced spirited dissent since returning to
the presidency for his third term, his critics have so far
failed to make significant inroads into his grip on power.

More than 81,000 people took part in the vote, underscoring
the scale of the challenge the opposition faces in a country
with a population of 142 million people.

After some bickering on Saturday, the new group of 45
leaders agreed to hold the next rally in December to mark the
anniversary of the first anti-Putin protests.

Opposition supporters shouted "Shame!" as police ushered
Navalny, Yashin and Udaltsov into police vans. The three were
released after several hours at the police station and face
fines of up to 30,000 roubles (about $1,000) or up to 50 hours
of community work for violating public order.

Their arrests followed the detention this month of activist
Leonid Razvozzhayev who said he was abducted in Ukraine and
tortured.

Kremlin critics in Russia and abroad say the detentions
signal a crackdown on dissent since Putin started his new term.

"Reports about new arrests of democratic opposition
activists in Moscow. Many signs points at a much harsher regime
attitude," Swedish Foreign Minister Carl Bildt wrote in his
Twitter microblog.

KREMLIN SCORNFUL

The Kremlin, which has so far ignored the opposition vote,
poured scorn on the Council's first session saying that the new
leaders were not capable of proposing a constructive agenda or
moving the country forward.

"The fact that the opposition is debating how to mark the
anniversary of its protests shows that they are looking into the
past, not the future," Interfax quoted Aleksei Chesnakov, one of
the leaders of pro-Kremlin party United Russia, as saying.

Sergei Mironov, leader of left-leaning Just Russia party
which holds 64 seats in the parliament, threatened to expel two
of his party members who were elected in the Council and said
anti-Kremlin protesters were turning into a sect.

Communist leader Gennady Zyuganov told his party congress
that he had warned leftist Udaltsov against siding with
"liberals" like Navalny and Yashin who dominate the Council.

Police said the three activists arrested on Saturday were
detained for public order violations. It said the protest was
not sanctioned by Moscow authorities, as required by law.

While pro-Kremlin television channels barely mentioned the
Coordinating Council meeting, they gave plenty of air time to
the launch of billionaire Mikhail Prokhorov's new party Civil
Platform which pledged to pursue a liberal economic agenda.

Prokhorov, a tycoon whose fortune is estimated by Forbes
magazine at $13 billion, said he will now hand over the
management of his business assets to partners and focus on
politics.

The businessman challenged Putin in the March election, but
critics said he had been picked by the Kremlin as a token
opposition figure. He collected almost 8 percent of the vote.

"From this day I will only engage in political activity and
nothing else," Prokhorov told his supporters. "There is an
opinion that here one can either be with the Kremlin or with the
Coordination Council. This is not true."